This invention relates to Nuclear Magnetic Resonance, and more specifically relates to Nuclear Magnetic Resonance Imaging.
Nuclear Magnetic Resonance (NMR) is well established as an analytical tool, and applications of NMR in the field of petrophysics have included well logging and laboratory measurements of free-fluid index, residual oil saturation, and permeability. These applications are based on NMR measurements of bulk nuclear spin density and various bulk spin relaxation times.
A relatively recent development in NMR is the technique of NMR Imaging, NMRI. In 1973, Lauterbur (P. C. Lauterbur, Nature, Vol. 242, Mar. 16, 1973, pp. 190-191) demonstrated that by applying controlled magnetic field gradients, the spatial distribution of hydrogen-containing fluids could be mapped with NMR. NMRI has been mostly employed in the field of medical imaging to provide a physician with the ability to discriminate between various normal and abnormal tissues. Nonmedical applications of NMRI, however, are just now being investigated.
Although NMR has been employed to measure some bulk petrophysical properties of materials, it has not been employed to determine the spatial variation of petrophysical properties. Further, most conventional methods for measuring the bulk petrophysical properties of a material do not employ NMR techniques but employ techniques that attempt to directly measure the petrophysical property and as a consequence are often time consuming and tedious. Some of these conventional techniques may introduce errors into the measurement because of the small size and number of most samples employed to make petrophysical measurements.
These and other limitations and disadvantages of the prior art are overcome by the present invention, however, and methods for nuclear magnetic reasonance imaging are provided for determining petrophysical properties of materials.